I have luck on both smelt and commercially frozen lake herring, also called ciscos or tullibies around here.
I think that the pike may go for the ciscos / lake herring first, in lakes that contain them naturally.
In lakes where there are no lake herring the smelts work fine.
Smets and lake herring /ciscos tend to float so you may need to puncture the swimbadder in order to get them to sink with out weights of some kind.
Like UfCreel said mackerel will also work.
Around here are generally fairly large compared to other frozen baits. They are also oily + they sink.
The type I use is called chub mackerel.
I have also caught them on regular frozen minnows, hotdogs, bits of squid as bait.
WW